Method of making an ingot mold stool

ABSTRACT

A cast iron ingot mold stool having a coating of granulated iron oxide particles fused into the upper surface thereof to prevent cast ingots from sticking thereto.

UnIted States, Patent 1191 1111 3,783,933 Leedy v Jan. 8, 1974 METHOD OFMAKING AN INGOT MOLD 1,920,244 8/1933 Connelly et al 164/97 STOOL2,204,453 6/1940 Siegert 164/97 3,454,385 7/1969 Amero..... 51/309 XInventor: Verne y, Palos g 3,093,464 6/1963 COeS 51/309 x 1 AssigneerUnited States Steel Corporation, FOREIGN PATENTS 0R APPLICATIONSplttsburlgh 2,011,199 2 1970 France 164/57 [22] Fil d; A 20, 19716,914,451 3/1971 Netherlands 249/204 [21] Appl' 173435 PrimaryExaminer-Robert D. Baldwin Assistant Examiner-JohnE. Roethel [52] US. Cl164/58, 164/97, 249/204 Att0rney-F0rest C. Sexton [51] Int. Cl B22d27/18 [58] Field of Search 249/204; 164/97,

164/57, 58; 72/42; 51/309 [57] ABSTRACT A cast iron ingot mold stoolhaving a coating of granu- 5 Referenc'es,v Cited lated iron oxideparticles fused into the upper surface UNITED'STATES PATENTS thereof toprevent cast ingots-from sticking thereto. 2,090,836 8/1937 Glezen164/97 4 Claims, 2 Drawing Figures 1 METHOD OF MAKING AN INGOT MOLDSTOOL BACKGROUND OF THE INVENTION Steel ingot molds usually consist ofupright cast iron mold shells open at the top and bottom. To close thebottom for casting ingots, the mold shell is placed on a thick cast ironmold stool.

ln stripping a steel ingot from the mold, considerable difficulty issometimes encountered because the ingot tends to stick to the cast ironmold stool, especially if the mold stool is new or reasonably new.Frequently the two are so firmly fused together that the mold stool mustbe broken free from the ingot. This of course results in excessive stoolcomsumption and costly time delays. Older mold stools, which have beenused through many heats, appear to have a highly corroded and oxidizedsurface to which the ingot does not readily stick. New, or near new,ingot mold stools, however, do not have such an extensive surfacecorrosion, and hence do have a tendency to fuse with the ingot casttherein.

To alleviate this problem, several procedures have been employed. Somemills for example spray the mold stool with various solutions which willdry to form a refractory surface. The success of these procedures israther limited because the molten steel will frequently wash away thecoating. As another example, some foreign mills have virtuallyeliminated the problem by using graphite mold stools. Graphite moldstools however are quite expensive and fragile and do not thereforealleviate the cost problem.

SUMMARY OF THE INVENTION An object of this invention is to provide a newand improved cast iron mold stool which will not stick or fuse to aningot cast thereon, and which is not significantly more expensive thanthe conventional cast iron mold stools of the prior art.

Another object of this invention is to provide a cast iron mold stoolhaving densev iron oxide surface layer to be exposed to the ingot metal.

A further object of this invention is to provide an improved cast ironmold stool which has a greater average life-span than conventional castiron mold stools of the prior art.

Still another object of this invention is to provide a method for makingthe improved cast iron mold stools of this invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a sectional elevation of themold stool of this invention; and

FIG. 2 is a sectional elevation ofa mold used to cast the ingot moldstool.

DESCRIPTION OF THE PREFERRED v EMBODIMENT With reference to FIG. 1, theingot mold stool of this invention is much like prior art mold stools inthat the main portion thereof comprises a rectangular cast iron block10. The one distinction, and the crux of this invention, is the coatingof dense iron oxide 12 cast into the upper surface thereof. Morespecifically, the oxide coating consists of granulated hemitite,magnetite or mixtures thereof, which is fused into the cast iron block10. Although the iron oxide coating 12 could extend over the entireupper surface of cast iron block 10, it

is preferred that it be limited to the general area which will come intocontact with molten steel. This is because the cast iron surface wearsbetter against the solid cold surfaces of the ingot mold, whereas theoxide surface is best only on areas in contact with molten metal.Although the thickness of the iron oxide coating is not critical, it ispreferable that it be at least about one-fourth inch thick so that itwill not be worn away too soon. Although thinner coatings would worksuitably, it is likely the coating would be eroded away too soon toafford suitable protection. On the other hand, it need not be thickerthan about one-half inch to work suitably.

The particle grain size of the oxide coating is not particularlycritical. It should of course not be so coarse as to provide a roughtexture which can be quickly and easily eroded away, and not so finethat it is dissolved by the molten cast iron. For all practicalpurposes,

grain sizes less than one-fourth inch and larger than about mesh arepreferred.

With reference to FIG. 2, the mold stool described above is castupside-down according to conventional practices directly over thegranular iron oxide layer 12. Specifically, a rectangular sand mold 20is formed within a molding flask 22. The granular iron oxide 12 is thengently compacted against the bottom surface 24 of sand mold 20. Althoughthe iron oxide 12 can cover the entire bottom surface 24, as notedabove, it is preferred that the iron oxide 12 cover only a rectangularportion in the center of bottom surface 24, generally limited to thatarea which will come into contact with molten steel during ingotteeming. In order to facilitate compaction of the iron oxide l2againstsurface 24, it is further preferred that some lateral retaining means orform be employed to contain the iron oxide 12 during compaction. Asshown, therefore, iron oxide 12, is gently compacted within a lowrectangular form 26 which resembles a thin picture frame. Since form 26serves only to provide temporary support during compaction of iron oxide12, it is removed thereafter so that the compacted iron oxide 12 is moreexposed to the iron cast thereagainst. Instead of a rectangular form 26,I have also successfully used expanded metal grids or screeens (notshown) into which the iron oxide 12 is compacted. In fact, the expandedmetal grid or screen probably works better than the rectangular frame 26since it provides channels through the iron oxide 12 into which themolten cast iron will flow to provide a better fusion bond therewith.Still another procedure is to provide a rectangular depression (notshown) into the bottom surface 24 of mold 20 and compacting the ironoxide 12 into the depression. When the oxide is so placed with orwithout the use of a retaining means, molten cast iron is poured intogate 28 until the mold is filled. The molten iron in the mold will fusewith the granular iron oxide 12.

As noted above, the oxide particles must be a dense form such ashemitite or magnetite so that it will not be dissolved or washed away bythe molten cast iron. I therefore prefer to use a granulated hemititeore concentrate which is readily available in many mills. The oreconcentrate I use has a density of about 200 lb./cu. ft., contains about5 percent silica, and has a typical screen analysis as follows:

Screen Cumulative 7: On l0 Mesh 2.6 2.6 On 20 Mesh 18.1 20.7

On 35 Mesh 33.7 54.4 On 60 Mesh 23.7 78.1 g On 80 Mesh .7 On lOO Mesh0.8 88.6

On 200 Mesh 9.3 97.9 Through 200 Mesh 2.1 l00.0

In use, the mold stool is placed on a car (not shown) with the oxidecoating 12 facing upward. An ingot mold (not shown) is placed on themold stool with the open bottom end thereof directly over the oxidecoating 12. As noted above, it is preferred that the ingot mold itselfrest directly on the cast iron block 10 and not on the coating 12.Molten steel is then teemed into the open top of the ingot mold andthere allowed to solidify. As with all mold stools, the molten steelwill erode away a small portion of the surface. However, since theprimary constituent of the oxide coating 12 is iron, the ingot is notcontaminated thereby. After the ingot has solidified, the ingot andingot mold can readily be lifted free of the mold stool for strippingwithout any appreciable sticking.

My ingot mold stools have now been used in the production of over 50,000ingots and never has there been any appreciable sticking. The iron oxidecoating 12, depending upon the thickness, will eventually be completelyeroded away by the molten steel. By that time, however, the mold stoolwill have been used a sufficient number of times to have the densecorrosion surface caused by repeated use, and hence there is still nosticking problem. Even though the oxide coating 12 is somewhatshort-lived, it does serve a very useful purpose in preventing stickingwhen the mold stool is new or relatively new, i.e., when sticking ismost likely to occur. In assisting the mold stools through this mostcritical period, the oxide coating 12 does substantially lengthen theaverage life span of the mold stools.

I claim:

1. A method of making ingot mold stools the steps comprising forming arectangular sand mold, gently compacting a layer of iron oxide particleson the bottom of said sand mold, casting molten cast iron into said sandmold causing the iron oxide particles to be fused into the surface ofthe cast iron adjacent thereto.

2. The method of claim 1 in which the bottom of said sand mold isprovided with a rectangular form and said iron oxide particles aregently compacted into said form, and the form thereafter removed.

3. The method of claim 1 in which the bottom of said sand mold isprovided with a rectangular expanded metal grid and said iron oxideparticles are gently com pacted into said grid, and the grid thereafterremoved.

4. The method of claim 1 in which the bottom of said sand mold isprovided with a rectangular depression and said iron oxide particles aregently compacted into said depression.

2. The method of claim 1 in which the bottom of said sand mold isprovided with a rectangular form and said iron oxide particles aregently compacted into said form, and the form thereafter removed.
 3. Themethod of claim 1 in which the bottom of said sand mold is provided witha rectangular expanded metal grid and said iron oxide particles aregently compacted into said grid, and the grid thereafter removed.
 4. Themethod of claim 1 in which the bottom of said sand mold is provided witha rectangular depression and said iron oxide particles are gentlycompacted into said depression.